A photoconductive process for electrophotographic light-sensitive materials consists of (1) a step of generating electric charges by exposing to light, and (2) a step of transporting the electric charges.
An example of a substance for conducting steps (1) and (2) in the same substance in a selenium light-sensitive plate. A combination of amorphous selenium and poly-N-vinylcarbazole can be used to conduct step (1) and (2) separately. By carrying out steps (1) and (2) with different substances respectively the substances used in the electrophotographic light-sensitive materials can be selected from a wide range and, consequently, electrophotographic characteristics of the electrophotographic light-sensitive materials, such as sensitivity or acceptable electric potential, etc. are improved. Further, substances suitable for producing the electrophotographic light-sensitive coating layer can be selected from a wide range.
Photoconductive substances in the electrophotographic light-sensitive materials now used for the electrophotographic process include selenium, cadmium sulfide and zinc oxide, etc.
In the electrophotographic process, as be disclosed in U.S. Pat. No. 2,297,691 by Carlson, a photoconductive material comprising a base coated with a substance which is insulating in the dark, the electric resistance of which varies according to an exposure applied during imagewise exposing to light, is used. This photoconductive material is generally charged first to give uniform surface electric charges in the dark after carrying out dark adaptation for a suitable time. This material is then imagewise exposed to light by a light pattern which has the effect of reducing surface electric charges according to relative energy included in various parts of the light pattern. The residual surface electric charges or latent images formed on the surface of the photoconductive material layer (electrophotographic light-sensitive layer) are brought into contact with a suitable electroscopic indication material, namely, a toner to obtain visible images.
The toner is contained in an insulating solution or a dry carrier. The toner will adhere to the surface of the electrophotographic light-sensitive layer according to the electric charge pattern. The adhered indication material can be fixed by a known means such as heat, pressure or solvent vapor, etc. Further, the latent images can be transferred to the second base (for example, paper or film, etc.). Likewise, the latent images can be transferred to the second base where they are developed. The electrophotographic process is one of such image forming processes.
In such an electrophotographic process, the basic characteristics required for the electrophotographic light-sensitive materials include: (1) the electrophotographic light-sensitive material can be changed in a suitable electric potential in the dark, (2) there is a low level of leakage of electric charges in the dark is at a low level, and (3) electric charges can be quickly discharged by light irradiation.
The above described inorganic substances used hitherto have many advantages but also have various disadvantages. For example, selenium widely used at the present sufficiently satisfies the above described requirements (1)-(3). However selenium is not desirable because production thereof requires maintaining difficult conditions which increase production cost, i.e., it is difficult to process it to make a long sheet because it has substantially no flexibility, and it is necessary to handle it with care because due to its sensitivity to thermal or mechanical impacts. Cadmium sulfide and zinc oxide are used as electrophotographic light-sensitive materials by dispersing in a resin binder, but they can not be repeatedly used, because they have mechanical disadvantages such as in smoothness, hardness, tensile strength or friction resistance, etc.
In the recent years, in order to remove the disadvantages of these inorganic substances, electrophotographic light-sensitive materials using various organic substances have been proposed and some of them have been put to practical use. Examples of such material include an electrophotographic light-sensitive material composed of poly-N-vinylcarbazole and 2,4,7-trinitrofluorenon-9-one (U.S. Pat. No. 3,484,237), an electrophotographic light-sensitive material in which poly-N-vinylcarbazole is sensitized with pyrylium salt type dyes (U.S. Pat. No. 3,617,268), an electrophotographic light-sensitive material containing an organic pigment as a main component (U.S. Pat. No. 3,898,084) and an electrophotographic light-sensitive material containing an eutectoid complex composed of a dye and a resin as the main component (U.S. Pat. Nos. 3,732,180 and 3,684,502), etc.
In these organic electrophotographic light-sensitive materials, the mechanical characteristics and flexibility of the above described inorganic electrophotographic light-sensitive material can be improved to certain extent. However, the material still do not sufficiently satisfy requirements for the electrophotographic light-sensitive material because they generally have a low light-sensitivity and are not suitable for repeated use.